Monoclonal antibodies have proved to be important reagents for the antigenic analyses of rotavirus proteins. Recently, these antibodies have been used extensively for the identification of VP7 serotype of rotavirus strains recovered from epidemiologic surveys and vaccine trials. Serotype identification of rotavirus field isolates is especially critical for surveys conducted during rotavirus vaccine trials. In addition, several monoclonal antibodies have been adapted in our laboratory for use in an epitope-blocking immunoassay in order to analyze antigenic site-specific antibody responses to infection with wild type rotaviruses or attenuated rotavirus vaccine strains. This technique is being utilized in the analysis of sera from rotavirus vaccine trials so that the immune responses important in vaccine induced protective efficacy can be identified.